how old is this grill m/n 972a s/n 601153800
Some manufacturers have a serial number lookup right on their site for finding this information out. Vulcan Hart does not unfortunately, so you'll have to contact them directly, toll-free, at 800-814-2028.
I can say that the Vulcan Hart 900A series is from the early-mid 1990s, based on their manuals.
Speaking of, here's an owner's manual, http://download.partstown.com/is-bin/intershop.static/WFS/Reedy-PartsTown-Site/-/en_US/manuals/VH-900A_iom.pdf
and here is a parts manual: http://download.partstown.com/is-bin/intershop.static/WFS/Reedy-PartsTown-Site/-/en_US/manuals/VUL-900A_pm.pdf
I hope this helps!
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